Separation of hydrocarbons from mixture thereof

ABSTRACT

A process for separating at least one component of aromatics, olefins, naphthenes and paraffins from a mixed hydrocarbon stock containing the same by means of extraction with solvent characterized in that a solvent system selected from the group consisting of N-acetyl-morpholine, mixed solvent of Nacetylmorpholine and water, N-acetyl-2-pyrrolidone, mixed solvent of N-acetyl-2-pyrrolidone with water, dimethyl sulfoxide, diethylene glycol and other organic solvent is employed.

United States Patent Akabayashi et al.

[ Aug. 1973 SEPARATION OF HYDROCARBONS FROM MIXTURE THEREOF Inventors:Hiroshi Akabayashi, Tokyo; Satoshi Hoshiyama, Ichikawa; ShinichiroTakigawa, Funabashi, all of Japan Nissan Kagaku Kogyo Kabushiki Kaisha,Tokyo, Japan Filed: Dec. 7, 1970 Appl. No.: 95,826

Assignee:

Foreign Application Priority Data Dec. 10, 1969 Japan 44/98926 June 29,1970 Japan 45/5670l US. Cl 208/314, 208/323, 208/326,

1111. c1 Cl0g 21/00 Field of Search 208/314, 322, 323, 208/326, 317

References Cited UNITED'STATES PATENTS 10 1940 Lyons 208/314 2,484,30510/1949 Mayland et al. 208/322 2,753,381 7/l956 Nelson 208/326 2,952,7l79/1960 Fleck et al..... 208/323 3,605,850 9/1971 Borst 208/325 PrimaryExaminer-Herbert Levine Att0rneyS.tevens, Davis, Miller & Mosher 57ABSTRACT diethylene glycol and other organic solvent is employed.

3 Claims, 3 Drawing Figures WATER 8 F LE HYDROCARBON FEED 13 AROMATIC 1PRODUCT 14 FX WATER l8 /-o121z1=m paooucr I 25 22 -1 l 2o 25 PARAFFIN LPRODUCT PATENTEDMIGZB ms SLY-55154 sum 1 use WATER HYDROCARBON FEEDAROMATIC PRODUCT OLEFIN PRODUCT 25 PARAFFIN PRODUCT PAIENTEUmsea ma3.755; 154

' sum 2 or 2 I-OLEFIN f CIB-HYDROCARBON soc c7- HYDROCARBON .8N'ACETYL'2- |GHT PYRROLIDONE n-PARAFFIN .2 .4 .e .8 N-ACET -2-N-ACETYL-Z-PYRROLIDONE,BY WEIGHT PYRROL' SEPARATION OF HYDROCARBONS FROMMIXTURE THEREOF The present invention relates to a process forseparating hydrocarbon mixtures into desired fractions by means ofextraction. More particularly, the present invention relates to aprocess for extracting desired fractions selectively from hydrocarbonmixtures containing olefins, naphthenes, paraffms and aromatics invarious proportions such as cracked petroleum oils or dehydrogenatedparaffinic hydrocarbons.

Petroleum hydrocarbons which have been subjected to conversiontreatments such as cracking contain olefins, naphthenes, paraffins andaromatic hydrocarbons in various proportions and, therefore, separationof the hydrocarbons into each fraction is demanded. Separation by meansof extraction with solvents having high selective solvent power foraromatic hydrocarbons such as N-methylpyrrolidone has been proposed and,benzene, toluene, xylene, etc. are isolated according to this process.

However, there has been no solvent having satisfactory selectivity forolefins, naphthenes and paraffins.

ln separation of olefinic hydrocarbons, absorption method in whichmolecular sieve or silica gel is used, a method in which a complex witha heavy metal is formed and extraction-distillation method have so farbeen employed. However, all of those methods are largely influenced byimpurities contained in the olefinic hydrocarbons and life of materialsused for the separation is short. Accordingly, those methods are tooexpensive and uneconomical to be employed in treatment of cheapby-produced oils such as oils obtained by petroleum treatments.

On the other hand, in condensation-separation of olefinic hydrocarbonsaccording to extraction with solvents, there has been proposed the useof liquid ammonia, liquid sulfurous acid, polyethylene glycols,sulfolan, dimethylsulfoxide and -butyrolactone. However, the solventsused on industrial scale have been those having only a relatively smallcarbon numbers (mainly those having five or less carbons). The reasonstherefor are that as carbon number is increased, selectivity of solventsis decreased or dissolving power is decreased even if the selectivity isexcellent. Thus, the solvents become very expensive and undesirable fromindustrial viewpoint.

An object of the present invention to provide a pro cess for collectingeffectively desired fractions according to extraction with a solventfrom olefin-containing hydrocarbon mixture by-produced in a large amountin thermal craking of petroleum or hydrocarbon mixtures containingolefins and paraffms obtained by dehydrogenation of paraffins.

Another object of the present invention is to provide extraction solventsystems which effectively extract desired fractions from saidhydrocarbon mixtures.

The above described objects and other objects of the present inventioncan be attained by using a solvent system selected from the groupconsisting of N- acetylmorpholine, mixed solvent of N- acetylmorpholineand water, N-acetyl-2-pyrrolidone, mixed solvent ofN-acetyl-Z-pyrrolidone and water or dimethylsulfoxide and mixed solventof N-acetyl-2- pyrrolidone and other optional organic solvent asextraction solvent for hydrocarbon mixtures containing variousproportions of aromatic hydrocarbons, olefinic hydrocarbons, naphthenehydrocarbons and paraffmic hydrocarbons.

The present invention will be understood more particularly by thefollowing descriptions including attached drawings.

FIG. I is a diagram showing steps in continuously performing the processof the present invention;

FIG. 2 is a triangular diagram showing mutual solubilities of l-olefin,n-paraffine and N-acetyl-Z- pyrrolidone; and

FIG. 3 is a triangular diagram showing mutual solubilities of aromatichydrocarbon, n-paraffme and N-acetyl-Z-pyrrolidone.

The inventors have found that anhydrous N- acetylmorpholine dissolvesolefin-naphthene hydrocarbons but its dissolving power for paraffmichydrocarbons is very poor and, therefore, it serves as effective solventfor extraction of olefin-naphthene hydrocarbons. I

The inventors have also found that N-acetylmorpholine in anhydrous statehas remarkably high dissolving power for aromatic hydrocarbons but itsselectivity is poor and that if five percent by weight of water isincorporated in N-acetylmorpholine, selectivity is improved though itsdissolving power is decreased and the selectivity is inclined to beincreased as water is increased. However, increase in amount of water islimited, since dissolving power of N-acetylmorpholine is graduallydecreased as water content is increased. Favorable water content is five20 percent by weight.

Since boiling point of N-acetylmorpholine is 243 C, this compound iscapable of extracting aromatic hydrocarbons having relatively highboiling points such as cymenes and cumenes in addition to benzene,toluene, xylene, etc.

Extraction with using hydrous N-acetylmorpholine as solvent can beperformed continuously in a counter current multistage extraction deviceat ambient temperature. Particularly, if reflux operation is added,aromatic hydrocarbons having a desired aromatic concentration can beobtained on the side of the extracting solvent and hydrocarbon mixturefree of aromatic hydrocarbons is obtained in the extraction residue.

The separation of olefin-naphthene hydrocarbons by means of extractionwith anhydrous N- acetylmorpholine is preferably effected after removalof aromatic hydrocarbons according to said method. However, if aromatichydrocarbon content is less than three percent by weight,olefin-naphthene hydrocarbons can be directly extracted withoutnecessity of previous removal of the aromatic hydrocarbons.

The extraction operation of olefin-naphthene hydrocarbons with anhydrousN-acetylmorpholine can be effected continuously by using a countercurrent multistage extraction device at ambient temperature. In caseolefin-naphthene hydrocarbons are to be extracted from hydrocarbonmixtures having more than eight carbon atoms, extraction temperature maybe elevated and solubilizing power may be increased. However, in anycase, a temperature not damaging selectivity of solvents is preferably.Olefin-naphthene hydrocarbons having relatively high purities can beextracted out by adding reflux operation to the aboveextractingoperation. In such a case, paraffinic hydrocarbons having apurity of near percent can be obtained as extraction residue.

According to our presumption, relation between water content ofN-acetylmorpholine and its solubilizing powers for xylene, heptene-l andn-heptane are as shown in Table 1.

TABLE 1 Solubilities in mixed solvent of Nacetylmorpholine and waterWater content Solubility Solubility Solubility of solvent of xylene ofheptene-l of N-heptane (8/ 8 (8 g (8/ g solvent) solvent) solvent) 0016.0 0 287.0 10.6 0 10 14.2 6.6 O 8.2 6.5 0 30 6.2 O 40 5.2 0 50 4.5 0

The extraction with N-acetylmorpholine can be effected either batchwiseor continuously. 1n continuous extraction, hydrocarbon mixture is firstintroduced in an aromatic extraction tower and an extract obtained bycounter current operation is fractionated into aromatic hydrocarbons,water and N-acetylmorpholine in an aromatic distillation tower.N-acetylmorpholine is reused by adding therein water and circulating itinto the aromatic extraction tower or by directly introducing it in anolefin extraction tower without adding water. On the other hand,extraction residue from the aromatic extraction tower is added with anecessary amount of water to washaway N-acetylmorpholine and then oillayer is introduced in the olefin extraction tower to extract olefins.After distillation or washing with water, olefins are obtained. The washwater can be reused by introducing it into the aromatic extractiontower.

In separating hydrocarbon mixtures according to extraction with asolvent such as N-acetylmorpholine, not only aromatic hydrocarbons andolefinic hydrocarbons but also aromatic hydrocarbons andolefin-naphthene hydrocarbons can be isolated at relatively highpurities from paraffinic hydrocarbons.

The process of the present invention will be illustrated more concretelyby way of examples.

Example 1 In 35.8 g (about 50 ml) of mixture of 20 wt. percent of xyleneand 80 wt. percent of n-heptane, 110.3 g (about 100 ml) ofN-acetylmorpholine having 5 wt.% water content are added at ambienttemperature. After thorough agitation for about 5 minutes, the solutionis allowed to stand whereby the solution is separated into two layers.The two layers are fractionated respectively. Thereafter, n-octane isadded as internal standard into the upper layer extraction residue andthe layer is analyzed according to gas chromatography. The results areshown in the following table.

Composition of Composition Proportion (wt. 17) hydrocarbons by weightn-hep- Xy- Sol- (wt.%) (91;) tane lene vent n-hepxylene tane Upper layer21.3 89.3 10.7 0 89.3 10.7 Lower layer 78.7 0.9 3.1 96.0 22.5

Example 2 Into 35.8 g (about 50 ml) of the same hydrocarbon mixture asin Example 1, 108.6 g (about 100 ml) of N- acetylmorpholine having 20wt. percent water content are added at ambient temperature. Afterthorough agitation for about 5 minutes, the solution is allowed to standwhereby the solution is separated into two layers. The two layers arefractionated respectively. Thereafter, n-octane is added as internalstandard into the upper layer (extraction residue) and the layer isanalyzed according to gas chromatography. The results are shown in thefollowing table.

Composition Composition of (wt. hydrocarbons Proportion (wt. by weightn-hep- Xy- 801- nxylene tane lene vent Heptane Upper layer 24.8 84.415.6 0 84.4 15.6 Lower layer 75.2 0 1.2 98.8 0 100 Example 3 Compositionof Composition hydrocarbons Proportion (wt. (wt. by weight p- 801- np(96) Hep- C yvent Hep- Cytane mene tane mene Upper layer 24.8 81.0 19.00 81.0 19.0 Lower layer 75.2 0 0.9 99.1 0 100 Example 4 Into 34.0 g(about 50 ml) of mixture of 20 wt. percent of heptene-l and wt. percentof n-heptane, l 10 g (about ml) of anhydrous N-acetylmorpholine areadded at 40 C. After thorough agitation for 5 minutes, the solution isallowed to stand whereby the solution is separated into two layers. Thetwo layers are fractionated respectively. Thereafter, n-octane is addedis added as internal standard into the upper layer (extractin residue)and the layer is analyzed according to gas chromatography. The resultsare shown in the following table.

Composition of Composition hydrocarbons Proportion (wt. (wt.%) by weightH n- Hep- Hepw Sol- Heptene-l tane l vent tane Upper layer 19.1 83.816.1 0.1 83.9 16.1 Lower layer 80.9 3.2 1.8 95.0 64.0 36.0

Example 5 lnto 37.4 g (about 50 ml) of hydrocarbon mixture containing 23wt. percent of dodecene-l and 77 wt. percent of n-dodecane, 109.8 g(about 100 ml) of anhydrous N-acetylmorpholine are added. After thoroughagitation at 80 C for about 5 minutes, the solution is allowed to standwhereby the solution is separated into two layers. The two layers arefractionated respectively. Thereafter, n-decane is added as internalstandard into the upper layer (extraction residue) and the layer isanalyzed according to gas chromatography.

The results are shown in the following table.

Composition Composition hydrocarbons Proportion (wt. (wt.%) by weightndode- Solndodededcenevent dodecene-l cane 1 cane Upper 22.4 81.3 [8.20.5 8L7 18.3 Lower layer 77.6 1.8 2.3 95.9 43.9 56.1

Example 6 Thermally cracked gasoline having boiling point.

range of 53 -l04 C, olefinic content of 38.3 vol.%, aromatic content of3.3 vol. percent and parafiinic content of 58.4 vol. percent wassubjected to continuous multistage extraction with N-acetylmorpholine inabout 3.0 liter multistage extraction device (40 stages) of rotatingdisk system under the following conditions:

Raw material-feeding speed: 366 g/hr. Raw material-feeding stage: 20thstage Solvent-feeding speed: 3,120 glhr. Temperature 40 C Rotating speedof disk: 600 r.p.m.

After extraction operation, extraction residue and extract wereseparated into the solvent and hydrocarbons by means of rectification.Thereafter composition of the hydrocarbon mixture was analyzed by FlAanalysis according to MS K 2536. PM is the Fluorescent IndicatorAdsorption and the JIS is the Japanese Industrial Standard for FM whichhas been published in 1969. The results are shown in the followingtable.

Hydrocarbon Com ition composition Weight (wt. (vol.%)

Hy- Sol- Ole- Par Aromag/hr. drovent fins aftics carbon fines Extractionresidue 95 100 1.1 98.9 0 pp layer) Extract (Lower 3390 8.0 92.0 51.544.0 4.5 layer) Example 7 Hydrocarbon mixture of 20 wt. percent oftoluene, 20 wt. percent of heptene-l and 60 wt. percent of nheptane issubjected to continuous extraction according to steps as shown in FIG.1.

The hydrocarbon mixture is fed into an aromatic extraction tower 2through 1 at ambient temperature (23 C). At the same time,acetylmorpholine having wt. percent water content is fed through a pipeand hydrocarbon mixture as reflux material containing 98 wt. percent oftoluene and 2 wt. percent of n-heptane is fed through a pipe ll.

Extraction product is fed into a standing tank 5 through a pipe 3 and adistillation tower 7 through a pipe 6. After distillation, distillatefrom the top of the tower is separated from water and fed in part intoan aromatic product tank through a pipe 8 and in part as reflux materialinto the 'aromatic extraction tower through the pipe 11. Extractionresidue which is known as ratfinate is introduced in a water tank 12through a pipe 4 and washed with water separated in the distillationtower 7 and freshly'fed water. Thereafter, the hydrocarbon mixture thuswashed with water is introduced in an olefin extraction tower l6 kept at40 C through a pipe 15. On' the other hand, water used for washing andthen separated in the water tank l2 is fed into an-extraction solventpreparation tank 13 through a pipe 14- and combined with bottomdistillate of the distillation tower 7 to'obtain 5 wt. percent watercontent which is again fed into the aromatic extraction tower 2 throughthe pipe 10.

Then, the hydrocarbon mixture introduced into the olefin extractiontower kept at 40 C is extracted with anhydrous N-acetylmorpholinesimultaneously introduced through a pipe 24 and reflux material(hydrocarbon mixture of 88 wt. percent of heptene-l, 11.5 wt. percent ofn-heptane and 0.5 wt. percent of toluene) introduced through a pipe 25.The extract is fed into a standing tank 19 through a'pipe l7 and into adistillation tower 21 through a pipe 20. After distillation, thedistillate from the top of the tower is sent in part into an olefinproduct tank through a pipe 22 and in part into the olefin extractiontower as reflux material through the pipe 25. The extraction residuewhich is known as raffinate is introduced into a water tank 26 through apipe 18 and washed with water separated in the distillation tower 7 andfreshly fed water. After completion of washing, the separatedhydrocarbons are sent into a paraffin product tank through a pipe 27. Onthe other hand, the wash water separated after being used for washing inthe water tank 26 is sent into the extraction solvent preparation tank13 through the pipe 14 and utilized partially. 7

Operation conditions employed in the above steps are shown in Table 2.Extracted quantities of toluene, heptene-l and n-heptane obtained in theextraction operation and compositions revealed according to gaschromatography are as shown in Table 3.

TABLE 2 Operation conditions in the aromatic extraction tower:

Multistage extraction device of ro- 10 stages tating disk system. Rawmaterial feeding 5th stage Raw material feeding speed 500 g./hr. Solventfeeding speed 1,810 g./hr. Reflux quantity 320 g./hr.

(feeding 1st stage) Operation conditions in the olefinic extractiontower:

Multistage extraction device of ro- 40 stages tating disk system. Rawmaterial feeding 20th stage Raw material feeding speed 402 g./hr.Solvent feeding speed 6,040 g./hr. Reflux quantity 965 g./hr.

(feeding 1st stage) TABLE 3 Aromatic Oiefinic Parafflnic product tankproduct tank product tank Quantity by weight, grams/ hour 290Composition, Toluene, 98.." Toluene, 2.7..." n-Heptnne, 99. weightpercent. Heptene-l,2.. He tone-1,873.. Heptene-1,l.0.

. neptene, 10.0.

The inventors have also found that N-acctyl-Z- pyrrolidone is quiteuseful as extraction solvent for olefins.

N-acetyl-2-pyrrolidone has the following structural formula:

This compound is in the form of colorless liquid having boiling point of236 C (760 mmHg) and specific gravity at room temperaure of 1.146. Thiscompound has a high thermal stability and is distillable under normalpressure or reduced pressure. This compound is completely compatiblewith water and its toxicity is low. N-acetyl-Z-pyrrolidone has a highdissolving power for hydrocarbon mixtures and, particularly, itdissolves out olefinic hydrocarbons selectively from mixture of olefinichydrocarbons and paraffinic hydrocarbons. FIG. 2 is a tri-angulardiagram showing mutual solubilities of l-olefin, n-paraffine andN-acetyl-Z-pyrrolidone. This figure clearly suggests thatN-acetyl-2-pyrro1idone has very excellent property as extraction solventfor olefinic hydrocarbons. There has been no compound in the past whichcan be used as solvent for olefinic hydrocarbons having such a widerange of carbon number.

As clearly shown in the figure, mutual solubility curve of a hydrocarbonhaving seven or less carbon atoms has so-called plate point at 25 Cwhich gives a closed curve against the axis connecting n-paraffin withn-acetyl-Z-pyrrolidone. Mutual solubility curve of a hydrocarbon havingeight or more carbon atoms at a temperature of at least room temperaturegives an open curve against the axis connecting n-paraffin with N-acetylpyrrolidone.

Thus, the solvent having the above mutual solubilities with an olefinichydrocarbon and a paraffinic hydrocarbon can be used effectively inindustrially various manners.

(1) For extracting olefinic hydrocarbons having seven or less carbonnumbers at a higher concentration, the triangular diagram of FIG. 2 canbe revised by incorporating therein another solvent for improvingselectivity of the solvent. Namely, the mutual solubility curve in FIG.2 is revised to an open curve against the axis connecting n-paraffinwith N-acetyl-Z-pyrrolidone so as to increase purity of the finalextract by olefinic hydrocarbon reflux material. As such solvents usedfor revision, water and dimethyl sulfoxide are most suitable. Proportionof those solvents to N-acetyl-Z-pyrrolidone is as shown in Table 1. Foran olefin having 7 carbon atoms, it is preferred to use a mixed solventcontaining less than 1.0 wt. percent of water or 3.0 20.0 wt. percent ofdimethyl sulfoxide.

TABLE 1 Solubility o1(g./100 g.

' solvent Content in mixed solvent (weight percent Heptenen-HeptaneWater w TABLEI [Solubllltles in mixed solvent 01 N-ocvtyl-Z-pyrrollrlonuand water or dimethyl SUllOXltltl (25 C.)]

Content in (2) In extraction of olefinic hydrocarbons having eight 10carbon atoms, the olefinic hydrocarbons of a high purity can be obtainedas the final extract by using only N-acetyl-Z-pyrrolidone alone.However, it is advantageous to use mixed solvent ofN-acetyl-Z-pyrrolidone and water or dimethyl sulfoxide for improvingselectivity and for economy of the extraction operation. In such a case,it is preferred to effect the extraction operation at a temperature inthe range of 40 60 C. Contents of water and dimethyl sulfoxide in themixed solvents are preferably 0.5 1.0 wt. percent and 1.0 5.0 wt.percent, respectively. Tables 2-1 and 2-2 show solubilities of al-olefin and an n-paraffin having 10 carbon atoms in mixed solvents ofvarious proportions at various temperatures.

TABLE 2-2.-SOLUBILITIES IN MIXED SOLVENT OF N- ACETYL-2-PYRROLIDONE ANDDIMETHYL SULFOXIDE Dlrnethyl sulfoxide content Solubility (g./i00 g.solvent) mixed ofsolvent (weight n-Decane Decene-l Temperature percent)(A) (B) (B)/(A) (3) As in the case of hydrocarbons having eight 10carbon atoms, olefinic hydrocarbons having 11 or more carbon atoms canbe treated with either N-acetyl-Z-pyrrolidone alone or mixed solvent ofN-acetyl-Z-pyrrolidone and water or dimethyl sulfoxide. If a mixedsolvent is to be used, it is necessary to elevate temperature in orderto increase solubility of the olefinic hydrocarbons. Tables 3-1 and 3-2show solubilities of a l-olefin and an n-paraffin having 11 and 13carbon atoms in N-acet-yl-Z- pyrrolidone and in mixed solvents atvarious temperatures.

Thus, olefinic hydrocarbons of a narrow carbon number range can befractionated and extracted from various hydrocarbon mixtures having awider carbon number range by using two or more extraction towers andproper combination of solvent mixture and temperatures.

TABLE 3-1.Solubillties Cu compounds in N-acetyl-2-pyrrolidoneand mixedsolvents Proportion by weight in mixed Solubility (gJlOO g. solvent(percent) solvent Temperature, Dimethyl n-Undec- Undec 0. Watersulfoxide ane (A) ene-l (B) (B)/(A) TABLE 32.Solubilities of C 1compounds in N-acetyl-2-pyrrolidone and mixed solvents Proportion byweig tin mixed Solubility (g./100 g. solvent (percent) solvent) ol-Tempern- Dirnethyl n-Tridec- Tridec ture, 0. Water sulloxide one (A)one-1(8) (B)/(A) 0 0 2. 8 9. l 3. 3 0 0 4. 5 ll. 9 2. 6 0 0 5. 2 l4. 02. 7 0 0 7. 0 23. 6 3. 4 l 0 7. 0 l1. 7 1. 7 5 0 5. 5 8. 0 1. 6 0 5 7. 515. 1 2. 0 0 10 7. 4 13. 5 1. 8 0 5 10. 4 21. 4 2. l 0 l0 9. 6 14. 9 l.6

Separation of olefinic hydrocarbons and solvent(s) from an extract canbe performed by rectification for hydrocarbons having 12 or less carbonatoms or and for ones having more 13 carbon atoms by allowing theextract to stand at room temperature and adding water in the solvent (s)till water content becomes higher than 5 wt. percent to separate thehydrocarbons. Those methods can be effected both in case of using onlyN-acetyl-Z-pyrrolidone and in case of using mixed solvent ofN-acetyl-2-pyrrolidone and water. The recovered water-containing solventcan be used as solvent for extraction of olefinic hydrocarbons having 12or less carbon atoms. In case of using mixed sovent ofN-acetyl-Z-pyrrolidone and dimethyl sulfoxide, hydrocarbons having l0 orless carbon atoms can be separated by rectification and hydrocarbonshaving 11 or more carbon atoms can be separated by allowing them tostand at room temperature and adding water so that water content in thesolvent to be recovered becomes less than 5 wt. percent. The recoveredwatercontaining mixed solvent canbe used as solvent for extraction ofolefinic hydrocarbons having 10 or less carbon atoms.

Thus, use of N-acetyl-2-pyrrolidone as extraction solvent for olefinichydrocarbons as in the process of the present invention is quiteefiective from industrial viewpoint.

N-acetyl-2-pyrrolidone used in the process of the present invention hasa high dissolving power also'for aromatic hydrocarbons and itsselectivity can e increased by incorporating therein various othersolvents. Thus, it be usable also as an extraction solvent for aromatichydrocarbons. More particularly, if N-acetyl-Z-pyrrolidone is used assolvent for hydrocarbon'mixture composed of olefinic, aromatic andparaffinic hydrocarbons, it exhibits a very high selectivity at anaromatic hydrocarbon content of less than 40 wt. percent and itselectively dissolves and extracts aromatic hydrocarbons. However, ifaromatic hydrocarbon is required to be concentrated to higher than 40wt. percent, it is preferred to use mixed solvent ofN-acetyl-2-pyrrolidone and another solvent such as water or diethyleneglycol.

Thus, the solvent according to the process of the present invention,N-acetyl-2-pyrrolidone, is quite excellent as a solvent for extractingaromatic hydrocarbons from hydrocarbon mixtures. Extracting effect ofN-acetyl-Z-pyrrolidone can be increased further by incorporating thereinanother solvent.

Aromatic'hydrocarbons have so far been fractionated by means ofextraction with various extraction solvents on industrial scale.Aromatic hydrocarbons such as benzene, xylene and toluene have actuallybeen fractionated according to this method. As known solvents used forthis extraction operation, there may be mentioned diethylene glycols,sulfolane liquid ammonia, dinitrile, cyano ether, y-butyrolactone,methylpyrrolidone and N-methyl-2-pyrrolidone.

Though all of those extraction solvents can be used as extractionsolvents for aromatic hydrocarbons, if those solvents are used, theextraction process becomes expensive due to their physical and chemicalstability or toxicity or other economical problems occur such as largerecovery loss of solvent.

After investigation on solvents more excellent than conventionalsolvents, the inventors have found that N-acetyl-2-pyrrolidone serves asa quite excellent solvent for extraction of aromatic hydrocarbons.

N-acetyl-2-pyrrolidone according to the present invention is capable ofselectively extracting aromatic hydrocarbons and this compound ischaracterized in that dissolving power at the time of extraction is veryhigh. Another feature of N-acetyl-Z-pyrrolidone is that this compound isalso capable of extracting durene, pseudocumene, various alkylbenzenesand polycyclic aromatic compounds such as high boiling compounds. forexample, tetralin and naphthalene in addition to benzene, toluene andxylene which have been obtained by means of extraction. Mutualsolubility curves of aromatic hydrocarbon, paraffinic hydrocarbon andN-acetyl-2-pyrrolidone are as shown in FIG. 3. Plate point of anyaromatic hydrocarbon resides at 25 C and, a closed curve is givenagainst the axis connecting n-paraffin with N-acetyl-Z-pyrrolidone.

Accordingly, N-acetyl-Z-pyrrolidone can be used as extraction solventfor almost all aromatic hydrocarbons. In case N-acetyI-Z-pyrrolidone isused for the purpose of concentrating aromatic hydrocarbons onindustrial scale, the above mutual solubility curve can be revised to anopen curve against the axis connecting n-parafi'm andN-acetyl-pyrrolidone by using mixed solvent of N-acetyl-2-pyrrolidoneand other selective solvent.

As such selective solvents which are useful in the form mixed withN-acetyl-Z-pyrrolidone, diethylene glycol, propylene glycol, sulfolane,dimethyl sulfoxide and N-methylpyrrolidone are suitable and, diethyleneglycol is particularly effective. Water can be also used as a componentof mixed solvent.

Proper extraction temperature when N-acetyl-2- pyrrolidone found by theinventors is used as extraction solvent is around room temperature(about 25 C). Heating or cooling is unnecessary at all. If theextraction is effected under heating, selectivity for aromaticextraction is lowered.

Aromatic hydrocarbons extracted with N-acetyI-2- pyrrolidone can beseparated completely from the solvent and thereby recovered either bydistillation or by adding water (if some water is already contained,water necessary for reducing solubility is added).

In separation of solvent and extract oil from extract layer, at least 95wt. percent of the extract oil can be separated by adding water in aquantity 0.8 1.5 times as much as the solvent.

In performing aromatic extraction operation on industrial scale by usingN-acetyl-2-pyrrolidone according to the present invention, roughly, thefollowing two steps can be employed.

(1) In case N-acetyI-Z-pyrrolidone is used for the purpose ofconcentrating out aromatic hydrocarbons from various hydrocarbonmixtures containing cracked petroleum oil and aromatic hydrocarbons, asolvent mixture containing 40 wt. percent of the diethylene glycol isintroduced into a multistage extraction tower and the hydrocarbonmixtures are refluxed till a desired concentration is obtained. Theextract phase in which the aromatic hydrocarbons are dissolved in aconcentrated form can be separated or recovered in a distillation toweror the extract phase can be separated into oil layer and solvent layerby adding therein water. Water can be separated from thewater-containing solvent by means of distillation insolventpurificiation step.

(2) In case hydrocarbons other than aromatic hydrocarbons such asolefinic hydrocarbons are to be concentrated by means of extraction fromvarious hydrocarbon mixtures including cracked petroleum oils andaromatic hydrocarbons, the aromatic hydrocarbons become undesirablecontaminant in the extraction operation and they are to be removed. Insuch a case N-acetyl-2-pyrrolidone (used alone but not in the form ofmixture) is very effective as extracting agent for pretreatment.Utilizing selective dissolving power of N-acetyl-2- pyrrolidone foraromatic hydrocarbons in a hydrocarbon mixture, extraction residueremaining not dissolved can be regarded to be hydrocarbon mixture hardlycontaining aromatic hydrocarbon compounds and the hydrocarbon mixturecan be regarded to be compounds from which industrially valuablehydrocarbons such as monoolefinic hydrocarbons can be extracted.

In view of the above steps, it is understood that N-acetyl-Z-pyrrolidonein the present invention can be used effectively for manner aromatichydrocarbons.

Solvent systems mainly composed of N-acetyl-2- pyrrolidone are capableof extracting naphthenic hydrocarbons contained in hydrocarbon mixturesin the same manner as in the case of extracting olefinic hydrocarbons.

Example 8 Into 38.0 g (about 50 ml) of mixture of 18.8 wt. percent ofheptene-l and 81.2 wt. percent of n-heptane, 1 16.0 g (about ml) ofmixed solvent of N-acetyl-2- pyrrolidone containing 5 wt. percent ofdimethyl sulfoxide are added at 25 C. After thorough agitation for about5 minutes, the solution is allowed to stand whereby the solution isseparated into two layers. The two layers are separated from each other.Thereafter, n-octane is added as internal standard into both upper layer(extraction residue) and lower layer (extract) and both layers areanalyzed according to gas chromatography. The results are shown in thefollowing table.

Composition of hydrocarbons Proportion Composition (wt.%) (wt. by weighthepn- 501- Hepntene hepvent tene hep -l tane -l tane Upper layer 19.414.3 79.8 5.9 l5.2 84.8 Lower layer 80.6 2.2 5.3 92.5 29.3 70.7 Example9 Into 38.1 g (about 50 ml) of mixture of 25.0 wt. percent of octene-land 75.0 wt. percent of n-octane, g (about 100 ml) ofN-acetyI-Z-pyrrolidone are added at 25 C. After thorough agitation forabout 5 minutes, the solution is allowed to stand whereby the solutionis separated into two layers. The two layers are separated from eachother. Thereafter, n-decane is added as internal standard into botyupper both (extraction residue) and lower layer (extract) and the layersare analyzed according to gas chromatography. The results are shown inthe following table.

Composition of hydrocarbons Proportion Composition (wt. (wt.%) bweightocnsol- Ocntene ocvent tene Oc- -l tane Upper layer 20.4 2L7 72.0 6.323.1 76.9 Lower layer 79.6 2.4 4.8 92.8 33.3 66.7

Example 10 Into 38.0 g (about 50 ml) of the same hydrocarbon mixture asin Example 8, 117 g (about 100 ml) of mixed solvent ofN-acetyl-Z-pyrrolidone containing 1 wt. percent of water are added at 25C. After thorough agitation for about 5 minutes, the solution is allowedto stand whereby the solution is separated into two layers. The twolayers are separated from each other. Thereafter, n-octane is added asinternal standard into both upper layer (extraction residue) and lowerlayer (extract) and both layers are analyzed according to gaschromatography. The results are shown in the following table.

Example 13 into 1 1.5 g of mixture of 24.4 wt. percent of durene, 51.7wt. percent of n-decane and 21.1 wt. percent of 5 decene-l 35.8 g ofN-acetyl-Z-pyrrolidone were added at 2 5 C. After thorough agitation'forabout 5 minutes, Proportion Composition (wt.%) (wt. the solution isallowed to stand whereby the solution is by welsh he? separated into twolayers. The two layers are separated (9b) tene hep vent tene hep i me Wefrom each other. The upper layer (extraction residue) pp l9 5 4 I 8 3 10and the lower layer (extract) are analyzed according to 83$; l gaschromatography. The results are shown in the follayer 80.5 2.2 4.6 93.232.4 67.6 lowing table.

Composition of hydrocarbons Iroppf- Composition (weight percent) (weightpercent) on Y weight Durn-Dec- Dec- 801- Durn-Dec- Dec- (percent) eneane ene-1 vent ene ane ene-1 Upper layer 10.1 14.3 60.4 21.2 4.1 15.063.0 22.0 Lower layer 83.9 4.5 3.8 2.2 89.5 42.8 36.1 21.1

Example 11 Example 14 into 38.5 g (about 50 ml) of hydrocarbon mixtureobtained by collecting straight chain hydrocarbons having 15 carbonatoms from cracked petroleum oil composed of 14.7 wt. percent ofolefins, and 85.3 wt. percent of paraffins, 119 g (about 100 ml) ofN-acetyLZ-pyrrolidone are added at temperatures given below. Afterthorough agitation for about 5 minutes, the solution is separated intotwo layers. The two layers are separated from each other. The upper andlower layers (extraction residue and extract, respectively) are analyzedaccording to gas chromatography. The results are shown in the followingtable.

Extraction on various mixture of n-parafi'in and aromatic hydrocarbon iseffected once in the same manner as in Examples 8 and 9 by using mixedsolution of N-acetyl-2-pyrrolidone and diethylene glycol. The resultsare as shown in the following table, wherein NAP showsN-acetyl-2-pyrrolidone and DEG shows diethylene glycol.

Example 15 into 50 ml of hydrocarbon mixture (cracked petroleum oil)having boiling point range of 76 144 C composed of 11.3 vol. percent ofaromatic hydrocarbons, 29.3 vol. percent of olefinic hydrocarbons andComposition of hydrocarbons Composition (weight Propor- (weight percent)percent) tion by weight Ole- Paral- Sol- Ole- Paraf- Temperature, 0.Layer (percent) fln fin vent fln fin Upper layer... 23.4 13.0 79.7 7.314.0 80.0 Lower layer-.- 76. 6 1.0 4. 1 94. 9 19. 6 80. 4

00 Upper layer... 22.8 12.3 80.5 7.2 13.3 86.7 Lower layer... 77. 2 1. 34. 7 04. 0 21. 7 78. 3

70 Upper layer.-- 21. 2 12.3 79.0 8. 7 13.5 86.5 Lower layer... 78. 8 1.4 5. 3 93. 3 20. 9 79. 1

Example 12 59.4 vol. percent of paraffinic hydrocarbons, 100 ml of Into14.5 g of mixture of 29.8 wt. percent of toluene and 70.2 wt. percent ofn-heptane, 45.4 g of N-acetyl- 2-pyrrolidone are added at 25 C. Afterthorough agitation for about 5 minutes, the solution is separated intotwo layers. The two layers are separated from each other. The upperlayer (extraction residue) and the lower layer (extract) are analyzedaccording to gas chromatography. The results are shown in the follow ingtable.

Composition of hydrocarbons Composition (wt. (wt. Proportion by weightTdnsoltolnuene hepvent uene heptane tane Upper layer 24.9 16.6 77.8 5.617.6 82.4 Lower layer 75.] 4.7 1.1 94.2 81.0 19.0

N-acetyl-Z-pyrrolidone containing 1 wt. percent of water are added at 40C. After thorough agitation for about 5 minutes, the solution is allowedto stand whereby the solution is separated into two layers. The twolayers are separated from each other. The upper layer (extractionresidue) and the lower layer (extract) are analyzed according to gaschromatography and HA (according to .11S-K-2536). The results are asshown in the following table.

Corn ition of hy rocarbons Proportion Composition (wt.%) (vol. b weighthyparafdrosol aroolefinic carvent matic tinbons ic Upper layer 14.8 87.013.0 0.9 33.7 65.4 Lower layer 85.2 13.4 86.6 20.6 25.4 54.0

Composition of Solvent hydrocarbons (g.) or Propor- Composition (weightpercent) (weight percent) raw tion by Composition of raw materialmateweight Soln-Hep- (weight percent) Solvent riel (g.) Layers (percent)Toluene n-Heptane vent Toluene tene Toluene, 70.5 NAP 90 34. Upper,layer.. 17. 9 57. 2 38.3 4.5 60.0 40. 0 n-Hept'ane, 29.6 DEG 11.9 Lowerlayer..- 82.1 9. 6 0.9 89. 6 91. 4 8. 6

n-Hep- Soln-Hep- Benzene tane vent Benzene tane Benzene, 43.4. NAP 7032.2 Upper layer... 13. 2 15.3- 80.0 4. 7 16. 1 83.9 n-Heptane, 66.6 DEG30 ll. 8 Lower layer... 86. 8 11. 0 5. 4 83.6 67. 0 33. 0

Oe- 801- Oe- Xylene tene-l vent Xylene tene-l Xylene, 44.0 NAP 70 32.8Upper layer... 13.0 23.1 60.5 16.4 27.6 72.4 Octene-l, 56.0 DEG 30 12.6Lower layer... 87. 0 10.4 8. 8 80.8 64. 2 45.8

Naphthan-Do- Sol- Nephthan-Dolene decene vent lene decane Naphthalene,31.4 NAP 70 34.0 Upper layer... 18.4 11. 1 87.1 1.8 11.3 88.7n-Dodecane, 68.6 12. 1 Lower layer.. 81. 6 7. 6 2. 2 90. 2 77. 6 22. 4

Example 16 0 We claim:

into 50 ml of hydrocarbon mixture having 10 carbon atoms (crackedpetroleum oil) composed of 17.0 vol. percent of aromatic hydrocarbons,30.2 vol. percent of olefinic hydrocarbons and 52.8 vol. percent ofparafiinic hydrocarbons, 100 ml of N-acetyl-2- pyrrolidone are added at60 C. After thorough agitation for about 5 minutes, the solution isallowed to stand whereby the solution is separated into two layers. Thetwo layers are separated from each other. The upper layer (extractionresidue) and the lower layer (extract) are analyzed according to gaschromatography and HA (according to JIS-K-2536). The results are asshown in the following table.

Composition of hydrocarbons Proportion Composition (wt.%) (vol. byweight hyarooleparafsoldromatic finfinic car vent ic bons Upper layer15.0 87.2 l2.8 9.5 29.6 60.9 Lower layer 85.0 16.6 83.4 23.2 30.6 46.2

Example 17 Composition of hydrocarbons Proportion Composition (wt.%)(vol. by weight hy- Solarooleparafdrovent matic fifinic carl'llC bonsUpper layer 17.4 87.0 [3.0 32.0 25.7 42.3 Lower layer 82.6 13.4 86.6 035.4 64.6

l. A process for separating at least one component of aromatics,olefins, naphthenes and paraffins from a mixed hydrocarbon stockcontaining the same, comprising extracting at least an aromatic orolefin compo nent with a mixed solvent of N-acetyl-2-pyrrolidone anddimethyl sulfoxide.

2. A process according to claim 1 in which a mixture ofN-acetyl-pyrrolidone and from l.0% to 5.0% by weight of dimethylsulfoxide based on the mixture is used.

3. A process according to claim 2 wherein the aromatics and the olefinsare extracted successively in separate extractors comprising,

a. feeding the mixed solvent and hydrocarbon stock into a continuouscountercurrent multistage aromatic extractor, separating the aromaticcontaining extract from an effluent from the aromatics extractor andrecovering the aromatics from said extract by distillation waterwashing,

recycling the separated solvent to the aromatic extractor,

recycling solvent which does not contain water to the olefin extractor,

washing the effluent from the aromatic extractor not containingaromatics with water,

b. passing the water washed effluent from the aromatic extractor notcontaining aromatics into the continuous countercurrent multistageolefin extractor, separating the olefin containing extract andrecovering the olefins from the solvent by distillation or waterwashing, recycling the recovered solvent to either the aromaticextractor or the olefin extractor, and recycling as additive water forthe solvent employed in the aromatic extractor the water used in washingthe effluent from the aromatic extractor and the water used when theextract from the aromatic extractor is washed.

* C I t t

2. A process according to claim 1 in which a mixture ofN-acetyl-pyrrolidone and from 1.0% to 5.0% by weight of dimethylsulfoxide based on the mixture is used.
 3. A process according to claim2 wherein the aromatics and the olefins are extracted successively inseparate extractors comprising, a. feeding the mixed solvent andhydrocarbon stock into a continuous countercurrent multistage aromaticextractor, separating the aromatic containing extract from an effluentfrom the aromatics extractor and recovering the aromatics from saidextract by distillation water washing, recycling the separated solventto the aromatic extractor, recycling solvent which does not containwater to the olefin extractor, washing the effluent from the aromaticextractor not containing aromatics with water, b. passing the waterwashed effluent from the aromatic extractor not coNtaining aromaticsinto the continuous countercurrent multistage olefin extractor,separating the olefin containing extract and recovering the olefins fromthe solvent by distillation or water washing, recycling the recoveredsolvent to either the aromatic extractor or the olefin extractor, andrecycling as additive water for the solvent employed in the aromaticextractor the water used in washing the effluent from the aromaticextractor and the water used when the extract from the aromaticextractor is washed.